1. Field of the Invention
This invention relates to a low temperature quick-setting type thermosetting insulating resin paste which is composed of a liquid epoxy resin, a setting agent, a setting accelerator and a filler, and which exhibits a very long pot life. More specifically, this invention relates to a non-solvent one-liquid type, resin paste for die bonding.
2. Description of the Prior Art
The remarkable present-day developments of the electronics industry has led to a rapidly increasing degree of circuit integration in semiconductor devices such as ICs and LSIs. At the same time, it has become possible to produce such semiconductor devices in large quantities. In view of the reduction in the prices of products utilizing such semiconductor devices, there is an urgent demand for increased efficiency and reduced cost in the mass-production of such products.
Conventionally, semiconductor parts are produced by die bonding semiconductor devices on lead frames and then sealing them with a hermetic seal. Since the original development of the method of sealing semiconductor devices with a thermosetting resin, it has become the practice to use a method of die bonding them with a conductive resin containing silver powder. This has contributed much to the enhancement of production efficiency and cost reduction.
At present, the die bonding process is generally performed using a conductive resin paste. However, in some types of chips including most MOS.ICs, metallization of the chip back surface can be dispensed with by drawing the sub-electrode out of the bonding pad on the chip. Accordingly, it is not necessary in such cases to employ an expensive conductive material for the die bonding resin, a relatively cheap non-conductive material being sufficient for the purpose. By using a non-conductive die bonding resin, a radical reduction in the total production cost becomes feasible.
As to the material for the lead frame, copper type materials are taking the place of the conventional 4,2-alloy because of the recent demand for further reductions in cost levels and improved thermal radiation characteristics necessitated by the increased power consumption of the chips used in many products. In this connection, a resin paste is needed which enables the bonding to be completed in a short time at a low temperature of 200 degrees C. or below, preferably 180 degrees C. or below, so that oxidation of the copper may be avoided.
However, most of the epoxy and polyimide resins conventionally used as die bonding resin pastes are generally set by heating in an oven, requiring a long setting time of ca. 30 minutes to 2 hours. Accordingly, it is impossible to conduct the process in which the resin paste is used as part of a production line. If such a resin paste were allowed to set in a short time at a high temperature (e.g. at 300 to 350 degrees C. for 20 to 30 seconds), voids might be generated due to vaporization of the paste components with relatively low boiling points such as solvents and reactive diluents. Further, decomposition of the epoxy resin might take place, resulting in the material being bonded becoming contaminated. Consequently, the idea of setting the resin paste rapidly at a higher temperature cannot be regarded as practical when one takes into consideration the above problems. It is naturally quite undesirable to set the resin paste at such a high temperature (300 to 350 degrees C.) when a copper type material is employed as the lead frame material.
Japanese Patent Laid-Open Nos. 59-149956 and 60-4521 disclose quick-setting type resin pastes aimed at having the setting process incorporated in a production line. However, most of these pastes require a setting temperature of 200 degrees C. or more. Even those which can be set at a temperature of 200 degrees C. or below, suffer changes in viscosity during use because of their short pot life, so that difficulty will be experienced when applying a given amount thereof to a lead frame.